1. Field of the Invention
The present invention relates to a suspension for a vehicle such as an automobile, and more particularly, to an active suspension for a vehicle adapted to operate coordinately in response to the centripetal force exerted to the vehicle body due to turning of the vehicle and a side force exerted to the vehicle body by a side wind.
2. Description of the Prior Art
Because of the flexibility required for the suspension of the vehicle, when the vehicle is turning the vehicle body makes a rolling around its center of rolling due to the torque and consisting of a couple of the centrifugal force acting through the center of gravity of the vehicle body and the corresponding centripetal force acting at the wheels from the road surface. Further, when a side wind blows against the vehicle, the vehicle body also makes a rolling around the center of rolling, because in the vehicles like automobiles the center of rolling is located at a relatively low position and therefore the total vector of the force applied by a side wind passes much above the center of rolling.
Although the control for suppressing the rolling of the vehicle body is to be based upon the roll angle acceleration applied to the vehicle body by turning of the vehicle and/or side wind blowing, considering that the rolling due to turning can be infallibly precisely forecast by detecting the lateral acceleration due to the centrifugal force, and noting that the relationship between the directions of the lateral acceleration and the roll angle acceleration due to turning is reversed from that due to a side wind, the present inventor once proposed to detect the lateral acceleration and the roll angle accelerating acting to the vehicle body by respective sensors, to discriminate the relative directions of the lateral acceleration and the roll angle acceleration thereby to know which of the turning and the side wind blowing is dominating to cause the rolling of the vehicle body, and to operate a plurality of suspension actuators so as to act against the force for rolling the vehicle body based upon the lateral acceleration when the turning is dominating, while operating the suspension actuators based upon the roll angle acceleration when the side wind blowing is dominating (Japanese Patent Application 21525/85, laid open as Publication 181715/86).
Thereafter, the present inventor further noted that a more improved steering performance is available if the degree of operation of the suspension actuators for the front wheels and that for the rear wheels can be differently distributed according to whether they are operated based upon the lateral acceleration or the roll angle acceleration, and proposed to operate the suspension actuators for the front and the rear wheels at a first distribution ratio of degree of operation such as Nf vs. Nr when they are operated according to the lateral acceleration, while operating the suspension actuators for the front and the rear wheels at a second distribution ratio of degree of operation such as Nf' vs. Nr' when they are operated according to the roll angle acceleration (Japanese Patent Application 295943/85; U.S. Pat. No. 4,712,807; European Patent Application 86101461).
However, in these former proposes the suspension actuators are still operated based upon only the lateral acceleration or the roll angle acceleration according to which of the turning or the side wind blowing is dominating, and therefore, when the effect of the turning on the rolling of the vehicle body is substantial but is overcome by that of the side wind blowing in the above-mentioned process of discriminating the directions of the accelerations, the merit of operating the suspension actuators based upon the lateral acceleration for the anti-rolling control is totally lost.